Heat-labile toxin of ETEC acts by which of the following mechanisms?
Attachment
B. Activation of adenylyl cyclase
C. Aggregative adherence
D. Ribosomal dysfunction
Long-term carriage and shedding is most likely to occur after gastrointestinal infection with which of the following species?
A. Escherichia coli O157:H7
B. Shigella dysenteriae
C. Vibrio cholerae
D. Salmonella typhi
11.液压传动的系统中常用的方向控制阀是()。
A. 节流阀
B. 溢流阀
C. 顺序阀
D. 换向阀
9.溢流阀一般是安装在( )的出口处,起稳压、安全等作用。
A. 液压缸
B. 液压泵
C. 换向阀
D. 油箱
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